Change of POI

[Bart B.]

Timing (or indexing) barrel curvature is done when fitting a barrel and is fairly popular practice with competition gunsmiths.

That may be. But a given barrel profile, bore and chamber dimensions will have the same metal compression and expansion stresses when horizontal regardless of any small curvature it may have when its axis is parallel with the force of gravity.

It's easy to measure how much the muzzle axis angle droops down due to the barrel's weight and length. Results will be within a few percent of what the formula calculates.

All barrel's droop when horizontal.

What happens to groups when curved barrels are clocked in to different hours?

 

[IdahoSharpshooter]

Quarter of a Century ago, I wrote for PS Magazine. I developed a working relationship with two engineers at Picatinny Arsenal. One of them told me; here's an example in layman's terms the average 4th grader can visualize. Cartoons used to show an Ostrich swallowing something kinda round thing. As the item went down that long neck, the cartoon showed the Ostrich's neck expanding around it. At high speed, the air in front of the projectile is compressed by the projectile as it passes down the barrel. At a certain speed (MV) the air cannot compress any further, and that pressure actually causes the barrel ID to expand a couple 100,000ths of an inch for a nano-second.
Makes sense...

 

[T-shooter]

I've no idea why the Bergers went right. I don't think it's due to bullets. Body torque during barrel times of both is virtually equal with both. Center of mass from recoil (bore) axis can cause horizontal group shift if different for each group

I wonder where another group of the AMAX ones would go.

After testing at 3 different times with powder charges from 41.6 to 42.8 grains of Varget (the 208g use 41.5g) and jumps from zero to .030", the Berger 200.20X all shoot low and to the right. I have shot 168g Sierra, 168g Hornady, and 208g Hornady several times and the windage never changes. The 208g usually needs 1/10 mil Left at 215 yards compared to the lighter bullets. These Bergers take 5/10 mil Left and 2/10 mil UP to get them on target compared to the 208 A-Max even though they are a little over 100 fps faster and grouping under 1/2 MOA so far. Both of the heavier bullets use Hornady brass and Federal Match primers.